Microelectromechanical device packages with integral heaters

ABSTRACT

A microelectromechanical device package with integral a heater and a method for packaging the microelectromechanical device are disclosed in this invention. The microelectromechanical device package comprises a first package substrate and second substrate, between which a microelectromechanical device, such as a micromirror array device is located. In order to bonding the first and second package substrates so as to package the microelectromechanical device inside, a sealing medium layer is deposited, and heated by the heater so as to bond the first and second package substrates together.

This application is a divisional of application Ser. No. 11/043,539,filed Jan. 25, 2005, which is a continuation of application Ser. No.10/443,318, filed May 22, 2003.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 10/443,318 to Tarn, filed May 22, 2003, the subjectmatter being incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention is generally related to the art ofmicroelectromechanical device packages, and more particularly, tospatial light modulators having micromirror device packages withintegral heaters.

BACKGROUND OF THE INVENTION

Micromirrors are key components of microelectromechanical system(MEMS)-based spatial light modulators (SLM). A typical MEMS-based SLMusually consists of an array of miniature micromirrors. Thesemicromirrors are selectively deflected, for example, in response to anelectrostatic force, which in turn selectively reflect incident light toproduce digital images. Such micromirrors, however, are extremelysensitive to contamination, such as moisture and dust. Thiscontamination has varying effects on the micromirrors, fromcapillary-condensation and post-release stiction to deterioration of themicromirror surfaces. Such effects can cause mechanical failure of themicromirrors in operation. For this and other reasons, micromirror arraydevices are often packaged after releasing.

Regardless of differences of the packaging methods currently developedfor a micromirror array device, two substrates, one for supporting thedevice and another one for covering the device, and sealing medium(s)for bonding the two substrates are utilized. Most of the sealing mediumsrequire application of heat during bonding. However, the heat, if notproperly applied, may degrade the micromirror array device. For example,improperly applied heat may change the desired mechanical properties ofthe micromirrors. It may also thermally activate particles, such asimpurities and particles making up the micromirrors, prompting diffusionof these activated particles within the micromirrors, thus exacerbatingdegradation of the micromirrors. Or heat may decrease anti-stictionmaterials within the package.

Therefore, a method and an apparatus are needed for packagingmicromirror array devices.

SUMMARY OF THE INVENTION

In view of the forgoing, the present invention provides an apparatus forpackaging micromirror array devices and a method of packagingmicromirror devices using the same. In order to package the micromirrordevice, a first and second substrate is provided. The micromirror arraydevice is accommodated within a cavity formed by the first and secondsubstrate. During packaging, one or more sealing mediums that areapplied between the first and second substrate are soldered by at leasta heater that is formed along the periphery of the surface of either thefirst or the second substrate and embedded underneath said surface ofsaid substrate. The first and the second substrates are then bondedthrough the soldered sealing mediums.

According to an embodiment of the invention, a substrate of a packagefor packaging a micromirror array device is provided therein. Thesubstrate comprises: a laminate that comprises a plurality of substratelayers bonded together; and a heater that is disposed along a peripheryof one substrate layer of the plurality of substrate layers and disposedbetween said substrate layer and another substrate layer of theplurality of substrate layers.

According to another embodiment of the invention, a package is provided.The package comprises: a first substrate having a heater along aperiphery of a surface of the first substrate and underneath saidsurface; a second substrate above the first substrate; a semiconductordevice or a microelectromechanical system device between the first andsecond substrate; and a first sealing medium layer between the firstsubstrate and the second substrate.

According to a further embodiment of the invention, a method ofpackaging a micromirror array device is disclosed. The method comprises:providing a first package substrate that comprises a heater integralwith and along a periphery of one surface of the first substrate;attaching a semiconductor device or a microelectromechanical device tothe first substrate; depositing a first sealing medium layer on thesurface of the first substrate; placing a second substrate on the firstsealing medium layer; driving an electric current through the heater soas to generate heat for melting the first sealing medium; and bondingthe first and second substrate by the melted sealing medium layer.

According to another embodiment of the invention, a system is provided.The system comprises: a light source for providing an incident light; aspatial light modulator for selectively modulating the incident light soas to form an image on a display target, wherein the spatial lightmodulator further comprises: a first package substrate having a heateralong a periphery of one surface of the first package substrate andembedded underneath said surface for generating heat; a micromirrorarray device held on the first package substrate; a second packagesubstrate on the first package substrate; a first sealing medium layerdeposited between the first and second package substrate; and whereinthe first and second package substrate is bonded together through thefirst sealing medium layer; a condensing optical element for directingthe incident light onto the spatial light modulator; a display target;and a projection optic element for directing the modulated light ontothe display target.

BRIEF DESCRIPTION OF THE DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 a is a diagram schematically illustrating a packaging substratefor packaging a micromirror array device, the packaging substrate havinga heater that is formed along the periphery of one surface of thesubstrate and embedded underneath said surface of said substrateaccording to an embodiment of the invention;

FIG. 1 b is a cross-sectional view of the package substrate of FIG. 1;

FIG. 2 a is a diagram schematically illustrating a packaging substratefor packaging a micromirror array device, the packaging substrate havinga heater formed along the periphery of one surface of the packagingsubstrate, and wherein the heater has a zigzag edge according to anotherembodiment of the invention;

FIG. 2 b is a cross-sectional view of the packaging substrate of FIG. 2a;

FIG. 3 is a diagram schematically illustrating a packaging substratehaving a heater that is laminated between two layers of said packagingsubstrate according to another embodiment of the invention;

FIG. 4 a is a diagram schematically illustrating a micromirror arraydevice that is packaged using a packaging substrate in FIG. 1 accordingto another embodiment of the invention;

FIG. 4 b is a cross-sectional view of the package in FIG. 4 a;

FIG. 5 a is a diagram schematically illustrating a micromirror arraydevice that is packaged using a packaging substrate in FIG. 1 accordingto yet another embodiment of the invention;

FIG. 5 b is a cross-sectional view of the micromirror array package ofFIG. 5 a;

FIG. 6 a is a diagram schematically illustrating a micromirror arraydevice that is packaged using a packaging substrate of FIG. 3 accordingto yet another embodiment of the invention;

FIG. 6 b is a cross-sectional view of the micromirror array device ofFIG. 6 a;

FIG. 7 is a diagram schematically illustrating a packaged micromirrorarray device;

FIG. 8 a is a simplified display system employing the packagedmicromirror array device of FIG. 7;

FIG. 8 b is a block diagram illustrating an exemplary operation of adisplay system employing three packaged micromirror array devices ofFIG. 7;

FIG. 8 c is a diagram schematically illustrating a display systememploying three packaged micromirror array devices of FIG. 7;

FIG. 9 a is a diagram schematically illustrating an exemplarymicromirror of the micromirror array;

FIG. 9 b is a diagram schematically illustrating an exemplarymicromirror array consisting of the micromirror of FIG. 9 a;

FIG. 10 a is a diagram schematically illustrating another exemplarymicromirror of the micromirror array; and

FIG. 10 b is a diagram schematically illustrating an exemplarymicromirror array consisting of the micromirror of FIG. 10 a.

DETAILED DESCRIPTION OF THE INVENTION

Turning to the drawings, the present invention is illustrated as beingimplemented in a suitable packaging process for micromirror arraydevices. The following description is based on selected embodiments ofthe invention and should not be interpreted as a limitation of theinvention with regard to alternative embodiments that are not explicitlydescribed herein.

Referring to FIG. 1 a, a packaging substrate with an integral heater forpackaging micromirror array devices is illustrated therein. As seen,packaging substrate 200 comprises substrate layer 210 and substratelayer 215. Substrate layer 210 has a concave surface that forms a cavityin which micromirror array device can be placed. On substrate layer 210,heater 220 is formed along the periphery of the concave surface ofsubstrate layer 210. Electric current from external electric powersource can be introduced into heater 220 via two leads 222 so as togenerating heat. Heater 220 is laminated between substrate layers 210and 215. A cross-sectional view of packaging substrate 200 isillustrated in FIG. 1 b.

In a preferred embodiment of the invention, heater 220 has a zigzag edgeas shown in FIG. 1 a. Alternatively, the heater can take any othersuitable forms, such as a set of consecutively connected straight lines(or disconnected lines each having leads at each end), coils orcombinations of lines and coils or zigzag lines. Other than forming theheater on substrate layer 210 which comprises a cavity for accommodatingmicromirror array devices, the heater can also be formed on substrate215. In particular, the heater can be formed on substrate 215 and on thesurface that faces substrate 210. As will be seen in FIG. 2 a, substrate215 is not necessary, and if not provided, preferably heater 220 ispatterned on or otherwise integral with substrate 210. The heater can bemade of any suitable materials, such as tungsten, and can be formed byany suitable methods (e.g. sputtering and electro-plating) for making athin film and standard methods (e.g. printing) for making a thick film.In order to generating heat, electric current is driven through the twoleads 222. Alternatively, the electric current can also be introducedinto the heater through leads 223, which are formed on substrate layer215 and connected to the two leads 222 respectively.

Substrate layers 210 and 215 can be any suitable preferablynon-electrically conducting materials, preferably ceramic or glass, andmore preferably ceramic. Other materials (e.g. organic or hybridorganic-inorganic materials) could also be used depending upon theirmelting points. In another embodiment of the invention, substrate layers210 and 215 each can be a multilayered structure that further comprisesa plurality of substrate layers. In this situation, the top layer, onwhich the heater is disposed, of substrate 210 and the bottom layer,which face the heater, of substrate 215 are preferably non-electricallyconducting. Other layers, including the substrate layers underneath thetop layer of substrate 210 and the substrate layers above the bottomlayer of substrate 215 can be any desired materials, such as ceramic,glass and metallic materials.

Other than embedding the heater underneath the surface of the packagingsubstrate, the heater can be formed on the surface of the packagingsubstrate as shown in FIGS. 2 a and 2 b. Referring to FIG. 2 a, theheater is formed along the surface of substrate 210, and no othersubstrate layer is formed thereon. Substrate 210 could be a multilayeredstructure. The heater is directly exposed to other materials, such assealing mediums, and structures, such as other packaging substrates. Inthis situation, the sealing medium deposited on the heater is preferablynon-electrically conducting materials, such as glass frit.

As discussed above, substrate layer 210 has a concave surface that formsa cavity in which micromirror array device can be placed. Alternatively,the substrate layers can be flat plates, as shown in FIG. 3. Referringto FIG. 3, substrate layers 266 and 262 of package substrate 260 bothare flat plates. Heater 220, which is formed on substrate layer 266 andalong the periphery of the surface of substrate layer 266, is laminatedbetween substrate layers 266 and 262. Similar to the heater in FIG. 2 a,an electric current can be driven through the heater via the two heaterleads 222 for generating heat.

Other than forming heater 220 on substrate layer 266, the heater canalso be formed on substrate 262. In particular, the heater can be formedon substrate 262 and on the surface that faces substrate layer 266.Similar to the substrate layers 210 and 215 in FIG. 2 a, substratelayers 262 and 266 can be any suitable non-electrically conductingmaterials, preferably ceramic and glass, and more preferably ceramic. Inanother embodiment of the invention, substrate layers 266 and 262 eachcan be a multilayered structure that further comprises a plurality ofsubstrate layers. In this situation, the top layer, on which the heateris disposed, of substrate 266 and the bottom layer, which faces theheater, of substrate 262 are preferably non-electrically conductinglayers. Other layers, including the substrate layers underneath the toplayer of substrate 266 and the substrate layers above the bottom layerof substrate 262 can be any desired materials, such as ceramic, glassand metallic materials. Micromirror array device 105 can be attached tosubstrate layer 262 and supported thereby.

In the following, exemplary implementations of the embodiments of thepresent invention will be discussed with reference to packages ofmicromirror array devices and packaging processes for making the same.It will be understood by those skilled in the art that the followingexemplary implementations are for demonstration purposes only and shouldnot be interpreted by any ways as a limitation. In particular, althoughnot limited thereto, the present invention is particularly useful forpackaging semiconductor devices or micromirror array devices. Thepackages with integral heaters and methods of using the packages withintegral heaters can also be applied in packaging othermicroelectromechanical systems, such as MEMS-based optical switches,image sensors or detectors and semiconductor devices requiring lowtemperature hermetic sealing. Moreover, the following exemplaryimplementation will be discussed with reference to heaters with zigzagedges and packaging substrate with substantially rectangular shapes forclarity and demonstration purposes only. Other variations of the heatersand the packaging substrates without departure from the spirit of thepresent invention may also be applicable. For example, the heater may becomposed of a set of segments with each segment being a straight line, acoil, a zigzag line or other desired forms. For another example, thepackaging substrate layers can be any desired shapes, other than thepreferred rectangular shape.

Referring to FIG. 4 a, a micromirror array device package using thepackaging substrate with an integral heater in FIG. 1 is illustratedtherein. Specifically, micromirror array device 105 is paced in thecavity of packaging substrate 200, which comprises integral heater 220as shown in FIG. 1. A double substrate type micromirror device isillustrated, however, as in all the drawings, a single substrate device(e.g. micromirrors formed on silicon wafer) could be used. Coversubstrate 235, which is preferably glass, is provided for sealing themicromirror array device within the cavity. In order to bond coversubstrate 270 and packaging substrate 200, sealing medium 230,preferably one that forms a hermetic seal and has a melting temperatureof 300° C. or less, and preferably 200° C. or less, is disposed betweenthe cover substrate and packaging substrate as shown. Preferably thesealing material is an inorganic material such as a metal, metal alloyor metal compounds (e.g. a metal or metalloid oxide). Alternatively,sealing medium layer 230 can also be deposited directly on the surfaceof packaging substrate 200, or on the surface of the lower surface ofcover substrate 235, in which case, sealing medium layer 230 ispreferably deposited along the periphery of the lower surface of thecover substrate. Sealing medium 230 is preferably a material that isstable, reliable, cost-effective and has good thermal-properties (e.g.co-efficient of thermal expansion (CET), thermal-conductivity etc.)compatible with the other components, such as package substrate 200 andcover substrate 235, of the micromirror array device package. It isfurther preferred that sealing medium has a low melting temperature(when the sealing medium is non-metallic) or soldering temperature (whenthe sealing medium is metallic). Glass frit, such as Kyocera KC-700, isan acceptable candidate for the sealing medium. During the bondingprocess, an electric current is driven through the integral heater viathe two heater leads (i.e. leads 222) for generating heat. The amplitudeof the electric voltage is dominated by electric characteristics of theheater (e.g. electric properties of the material of the heater, theshape of the heater), thermal characteristics and geometry of thesubstrate layers of packaging substrate 200 and the desired temperatureon the surface of packaging substrate 200 for melting sealing medium(e.g. sealing medium layer 230). As an example, the melting temperature,also the desired temperature on the surface of packaging substrate 200,of sealing medium 230 is from 100 to 300° C., preferably around 350° C.The heater is embedded underneath the surface of the packaging substrateat a distance preferably from 1 millimeter to 10 millimeters, preferablyaround 7 millimeters. In this example, the packaging substrate isceramic. Then the voltage set up between the two heater leads 222 ispreferably from 40 to 100 volts, preferably around 70 volts. In otherwords, this voltage causes the heater generating heat with an amountthat raises the surface temperature of the packaging substrate to themelting temperature of sealing medium layer 230. As a result, sealingmedium is melted and used to bond cover substrate 235 and packagingsubstrate 200. Meanwhile, the temperature at the micromirror devicelocation is far less than the temperature that causes mechanical failureof the micromirrors of the micromirror device. In the embodiment of theinvention, the temperature at the micromirror device location ispreferably less than 70° C.

During the bonding process, external pressure may be applied to thecover substrate, as shown in FIG. 4 b, wherein a cross-sectional view ofFIG. 4 a is illustrated therein. After a predetermined time period whenthe cover substrate and the packaging substrate are securely bonded, thevoltage, as well as the external pressure, can be withdrawn, but notnecessarily at the same time. As shown in FIG. 4 b, one or more getters325 can be provided within the package 270 for absorbing moistures andimpurity particles (e.g. organic particles) either sealed within thecavity or emitted from the components of package 270 during thepackaging process, especially during the heating process.

Though cover substrate 235 it is preferably visible light transparentglass, it may also be other materials, such as metals or materials thatare not transparent to visible light. In these cases, cover substrate235 preferably comprises an inlay light transparent glass for allowinglight to travel through and shine on micromirror array device 105.Alternatively, cover substrate 235 may have an opening forming windowwith a light transparent glass mounted on the window for allowingtransmission of incident light. Moreover, a light blocking mask withlight blocking strips formed around the circumference of the mask may beapplied along cover substrate 235 for blocking incident light notshining on the surface of the micromirror array device. By this, opticalperformance, such as contrast ratio, of the micromirror array device canbe improved.

Other than using glass frit as sealing medium, other suitable materials,such as solderable metallic materials, such as Au, BiSn_(x), AuSn_(x),InAg_(x), PbSn_(x), and copper, may also be used. However, mostsolderable metallic materials have poor adhesion to oxide materials orlayers that often form on surfaces of the substrates. To solve thisproblem, a metallization film is preferably employed to metalizing thesurface of the substrate before using solderable metallic sealingmediums, which will be discussed in further detail in the following.

Referring to FIG. 5 a, sealing medium layer 245 comprises a solderablemetallic material that is preferably stable, reliable, cost-effectiveand has thermal-properties (e.g. co-efficient of thermal expansion(CET), thermal-conductivity etc.) compatible with the other components,such as package substrate 200 and cover substrate 235, of themicromirror array device package, and more preferably has a lowsoldering temperature. In order to enhancing adhesion of sealing mediumlayer 245 to the surfaces of substrates 235 and 200, metallizationlayers 240 and 250 are provided for metalizing the lower surface ofcover substrate 235 and top surface of package substrate 200,respectively. Metallization mediums can be any suitable materials, suchas aluminum, gold, nickel or composition of two or more of suitablemetallic elements, such as gold/nickel, preferably a material with lowsoldering temperature. These materials can be deposited on the surfacesas thick or thin films using suitable deposition methods, such as thosestandard methods (e.g. sputtering) for depositing thin film and thosestandard methods (e.g. print and paste) for depositing thick films. Inan embodiment of the invention, metallization medium layer 250 is a thinlayer of noble metallic material, such as gold. This metallizationmedium layer is preferably deposited, such as sputtered as a film on thelower surface of cover substrate 235. Similarly, another metallizationlayer 240 is provided between sealing medium layer 245 and packagesubstrate 200 for metalizing the top surface of the package substrate.Metallization layer 240 is also preferably deposited, such as sputteredas a film on the upper surface of package substrate 200. Whenmetallization layers 250 and 240 are respectively deposited on the lowersurface of cover substrate 235 and the upper surface of substrate 200,these metallization layers may have high soldering temperatures. In thissituation, theses metallization layers are integral with cover substrate235 and substrate 200, respectively. Alternatively, metallization layers250 and 240, each could be a multilayered structure. As an example, themultilayered structure comprises a metal-oxide layer (e.g. CrO₂ andTiO₂), a metallic layer (e.g. Cr and Ti), a second metallic layer (e.g.Ni) and a third metallic layer (e.g. Au) on top. The metal-oxide layeris first deposited on the surface of the non-metallic substrate, such asceramic and glass, because it presents strong adhesion to thenon-metallic substrate's surface, which is generally oxidized. Themetallic layer generally comprises a metallic material that has strongadhesion to the metallic-oxidation layer. The second metallic layer isdeposited between the third metallic layer and the first metallic layerto prevent diffusion of the first metallic material into the thirdmetallic layer on top. As another example, metallization layer 240further comprises a tungsten layer, a nickel layer and a gold layer. Ofcourse, metallization medium layer 250 may also be a multilayeredstructure that further comprises a plurality of metallization layers asdesired. The third metallic layer on top, preferably comprises ametallic material having low oxidation. Exemplary metallic materials forthe third metallic layer are, Au, Cr and other noble metals.

During the packaging process, the integral heater embedded underneaththe surface of package substrate 200 is electrically powered forgenerating heat so as to solder sealing medium layer 245 betweenmetallization layers 240 and 250. Meanwhile, external pressure may beapplied to the package for enforcing bonding package substrate 200 andcover substrate 235, as shown in FIG. 5 b.

In another embodiment of the invention, cover substrate 235 may alsohave a heater. As the heater (e.g. heater 220) in package substrate 200as described with reference of FIG. 1 a, the heater in cover substrate235 can be formed along the periphery of the surface of the coversubstrate and embedded underneath said surface of the cover substrate.This heater in the cover substrate can be used in bonding the coversubstrate and the package substrate. And it is especially useful insoldering metallization medium layer 250 and sealing medium layer 245.

A cross-section view of package 275 in FIG. 5 a is illustrated in FIG. 5b. As seen, other features, such as getters 325 can be provided forabsorbing moisture.

Referring to FIG. 6 a, a micromirror array device package using thepackage substrate as shown in FIG. 3 according to further embodiment ofthe invention is illustrated therein. As seen, package substrate 300 isa flat plate with integral heater 220 embedded underneath the surface ofthe package substrate. Micromirror array device 105 is attached to andsupported by the package substrate. Spacer 310 is placed on the packagesubstrate and forms a space along with package substrate 300 foraccommodating the micromirror array device. Cover substrate 320 isplaced above the spacer and the package substrate. In order to bondingthe package substrate, the spacer and the cover substrate into amicromirror array device package, sealing medium layers 315 and 305 areprovided between the cover substrate and the spacer, and between thespacer and the package substrate, respectively. In the embodiment of theinvention, package substrate 300 and spacer 310 are ceramic.Alternatively, spacer 310 can be, Kovar, Invar, and NiFe_(x). And coversubstrate 320 is light transparent glass. Sealing medium layers 315 and305 are glass frit. During the packaging process, heater 220 iselectrically powered for generating heat so as to melt sealing mediumlayers 305 and 315. Alternatively, external pressure (not shown) can beapplied to enforcing the bonding.

As an alternative feature of the embodiment, another heater can beformed in cover substrate 320. The same as the heater in packagesubstrate 300, another heater can be formed along but underneath thesurface of the cover substrate. This heater can be electrically poweredfor generating heat during the packaging process so as to solder sealingmedium layer 315. When the sealing medium layer 315 is metallicmaterial, the heater of cover substrate 320 can be formed on the surfaceof the cover substrate for producing heat so as to soldering sealingmedium 315.

In another embodiment of the invention, the cover substrate, the spacerand the package substrate can be bonded using solderable metallicsealing mediums. In this situation, sealing medium layers 315 and 305each can be a combination of two metallization layers (e.g.metallization layers 250 and 240 in FIG. 5 a) and a sealing medium layer(e.g. sealing medium layer 245 in FIG. 5 a) disposed between the twometallization layers. Alternatively, each of the metallization layers ofthe combination can be a multilayered structure that further comprises aplurality of metallization layers. As an example, each sealing mediumlayer 315 or 305 can be a combination of a Au (or Al) layer and a Kovar(or Invar) layer and a Au (or Al) layer, or a combination of a Au (orAl) layer and a Kovar (or Invar) layer and a multilayered structure thatfurther comprises a Au layer and a Nickel layer and a tungsten layer.

As discussed above, cover substrate 320 is glass for allowing incidentlight traveling through to shine on the micromirror array device.Alternatively, the cover substrate can be a ceramic or metallic materialor any other desired materials that are not transparent to visiblelight. In this case, the cover substrate comprises a window with inlayglass for allowing incident light passing through. Alternatively, aglass plate may be mounted on the window of the substrate that is notincident light transparent. As a further alternative feature of theembodiment, a light blocking mask (e.g. a rectangular frame) that blocksincident light around the periphery of the micromirror array device isattached to the surface of the cover substrate, or directly painted orotherwise deposited around the circumference of the cover substrate.This is particularly useful when the cover substrate is glass.

Other than the flat shape, the cover substrate can be a concave covercap (not shown) with the lower surface of the cover substrate extendedtowards the opposite surface (e.g. the top surface) of the coversubstrate. In this case, the cover cap and package substrate 300 canform a space for housing the micromirror array device without spacer310. Accordingly, the number of metallization medium layers and thenumber of sealing medium layers can be reduced, and bonding process canbe simplified. For example, when cover substrate 320 that is a cover capand package substrate 300 is provided for housing micromirror arraydevice 105, packaging processes described with reference to FIGS. 4 aand 5 a can be directly applied herein.

Referring to FIG. 6 b, a cross-sectional view of the micromirror arraypackage in FIG. 6 a is illustrated therein. In addition to the packagingsubstrate, the cover substrate, the sealing medium layer and themetallization medium layers, getters may also be formed within thepackage. The cover light transmissive substrate need not be parallel tothe lower substrate, and the micromirror array device, such as set forthin U.S. patent application Ser. No. 10/343,307, filed on Jan. 29, 2003to Huibers, the subject matter of which being incorporated herein byreference.

The micromirror array package of the present invention has a variety ofapplications (e.g. maskless lithography, atomic spectroscopy, masklessfabrication of micromirror arrays, signal processing, microscopy, imagesensors/detectors and CCDs etc), one of which is in display systems.FIG. 7 illustrates an exemplary micromirror array package according toan embodiment of the invention. The micromirror array device is bondedwith in the package for protection. Incident light can travel throughthe cover substrate and shin on the micromirrors of the micromirrorarray device. This package can then be employed in practicalapplications, one of which is display systems.

Referring to FIG. 8 a, a typical display system employing a micromirrorarray device package of FIG. 7 is illustrated therein. In its very basicconfiguration, the display system comprises light source 102, opticaldevices (e.g. light pipe 104, lens 106 and 108), color wheel 103,display target 112 and spatial light modulator 110 that uses micromirrorarray device package of FIG. 7. Light source 102 (e.g. an arc lamp)directs incident light through the color wheel and optical devices (e.g.light pipe 104 and object lens 106) and shines on spatial lightmodulator 110. Spatial light modulator 110 selectively reflects theincident light toward optical device 108 and results in an image ondisplay target 112. The display system can be operated in many ways,such as those set forth in U.S. Pat. No. 6,388,661, and U.S. patentapplication Ser. No. 10/340,162, filed on Jan. 10, 2003, both toRichards, the subject matter of each being incorporated herein byreference.

Referring to FIG. 8 b, a block diagram illustrating a display systememploying three spatial light modulators, each having a micromirrorarray device package of FIG. 7, is shown, wherein each spatial lightmodulator is designated for respectively modulating the three primarycolor (i.e. red, green and blue) light beams. As shown, light 174 fromlight source 102 passes through optical filters 176 and is split intothree primary color light beams, that is, red light 176, green light 178and blue light 180. Each color light beam impinges a separate spatiallight modulator and is modulated thereby. Specifically, red light 176,green light 178 and blue light 180 respectively impinge spatial lightmodulators 182, 184 and 186 and are modulated. The modulated red light188, green light 190 and blue light 192 are recombined at light combiner194 for forming modulated color images. Combined color light 196 isdirected (e.g. by projection lens) onto display target 112 for viewing.A simplified display system based on the block diagram of FIG. 8 b ispresented in FIG. 8 c.

Referring to FIG. 8 c, the display system employs a dichroic prismassembly 204 for splitting incident light into three primary color lightbeams. Dichroic prism assembly comprises prisms 176 a, 176 b, 176 c, 176d, 176 e and 176 f. Totally-internally-reflection (TIR) surfaces, i.e.TIR surfaces 205 a, 105 b and 205 c, are defined at the prism surfacesthat face air gaps. The surfaces 198 a and 198 b of prisms 176 c and 176e are coated with dichroic films, yielding dichroic surfaces. Inparticular, dichroic surface 198 a reflects green light and transmitsother light. Dichroic surface 198 b reflects red light and transmitsother light. The three spatial light modulators, 182, 184 and 186 arearranged around the prism assembly. Each spatial light modulatorcomprises a micromirror array device package of FIG. 7 for modulatingincident light.

Regardless of whether the optical system utilizes a single micromirrorarray package as in FIG. 8 a, or multiple micromirror array packages asin FIGS. 8 b and 8 c, reflection from light transmissive substrates ispreferably minimized. In operation, incident white light 174 from lightsource 102 enters into prism 176 b and is directed towards TIR surface205 a at an angle larger than the critical TIR angle of TIR surface 205a. TIR surface 205 a totally internally reflects the incident whitelight towards spatial light modulator 186, which is designated formodulating the blue light component of the incident white light. At thedichroic surface 198 a, the green light component of the totallyinternally reflected light from TIR surface 205 a is separated therefromand reflected towards spatial light modulator 182, which is designatedfor modulating green light. As seen, the separated green light mayexperience TIR by TIR surface 205 b in order to illuminate spatial lightmodulator 182 at a desired angle. This can be accomplished by arrangingthe incident angle of the separated green light onto TIR surface 205 blarger than the critical TIR angle of TIR surface 205 b. The rest of thelight components, other than the green light, of the reflected lightfrom the TIR surface 205 a pass through dichroic surface 198 a and arereflected at dichroic surface 198 b. Because dichroic surface 198 b isdesignated for reflecting red light component, the red light componentof the incident light onto dichroic surface 198 b is thus separated andreflected onto spatial light modulator 184, which is designated formodulating red light. Finally, the blue component of the white incidentlight (white light 174) reaches spatial light modulator 186 and ismodulated thereby. By collaborating operations of the three spatiallight modulators, red, green and blue lights can be properly modulated.The modulated red, green and blue lights are recollected and deliveredonto display target 112 through optic elements, such as projection lens202, if necessary.

Referring to FIG. 9 a, an exemplary micromirror device of themicromirror array device is illustrated therein. As seen, micromirrorplate 136 is attached to hinge 155. The hinge is held by posts 152 thatare formed on substrate 120. With is configuration, the micromirrorplate can rotate above the substrate along the hinge. As alternativefeature, two stoppers are formed for controlling the rotation of themicromirror plate. The substrate is preferably glass. Alternatively, thesubstrate can be a semiconductor wafer, on which standard DRAM circuitryand electrodes can be constructed. FIG. 9 b illustrates a micromirrorarray comprising a plurality of micromirror devices in FIG. 9 a. Thearray is formed on the upper substrate which is preferably lighttransparent glass. The lower substrate, which is preferably asemiconductor wafer, is formed thereon an array of electrodes andcircuitry for electrostatically controlling the rotation of themicromirrors in the upper substrate. Other than forming the micromirrorarray and the electrode and circuitry array on different substrates asdiscussed above, they can be fabricated on the same substrate.

FIGS. 9 a and 9 b illustrate an exemplary micromirror device having amicromirror plate with zigzag edges. This is not an absoluterequirement. Instead, the micromirror plate can be of any desired shape.Another exemplary micromirror device with a different configuration isillustrated in FIG. 10 a. Referring to FIG. 10 a, the micromirror platehas a “diamond” shape. The hinge is arranged parallel to but off-setfrom a diagonal of the micromirror plate. It is worthwhile to point outthat the hinge structure has an arm that is extended towards one end ofthe micromirror plate. The entire hinge structure and the hinge areformed underneath the micromirror plate. This configuration has manybenefits, such as reducing the refraction of the incident light by thehinge and the hinge structure. FIG. 10 b illustrates an exemplarymicromirror array device composed of a plurality of micromirror devicesof FIG. 10 a.

As discussed above, sealing medium layers, such as layer 230 in FIG. 4 aand layer 245 in FIG. 5 a, are preferably layers that comprise materialswith low melting or soldering temperatures. In fact, other suitablematerials with relatively high melting or soldering temperatures mayalso be used. In this situation, external cooling mechanisms, such ascooling plates can be employed for dissipating heat from the package.For example, a cooling plate can be attached to substrate 200 in FIG. 4a and FIG. 4 b. Moreover, the present invention is not only useful inlow temperature packaging applications, but also in high temperaturepackaging applications.

It will be appreciated by those skilled in the art that a new and usefulmicromirror array package and methods of applying the same for packagingmicromirror array devices have been described herein. In view of themany possible embodiments to which the principles of this invention maybe applied, however, it should be recognized that the embodimentsdescribed herein with respect to the drawing figures are meant to beillustrative only and should not be taken as limiting the scope ofinvention. For example, those of skill in the art will recognize thatthe illustrated embodiments can be modified in arrangement and detailwithout departing from the spirit of the invention. In particular, otherprotective materials, such as inert gas, may be filled in the spaceformed by the package substrate and the cover substrate. For anotherexample, the package substrate, as well as the cover substrate and thespacer, can be other suitable materials, such as silicon dioxide,silicon carbide, silicon nitride, and glass ceramic. For yet anotherexample, other suitable auxiliary methods and components, such asapplications of Infrared Radiation during bonding for soldering thesealing medium layers, and pillars or other structures for aliening thesubstrates are also applicable. Moreover, other desired materials, suchas anti-stiction material, preferably in vapor phase for reducingstiction of the micromirrors of the micromirror array device, may alsobe deposited inside the package. The anti-stiction material can bedeposited before bonding the cover substrate and lower substrate. Whenthe cover substrate (e.g. cover substrate 235 in FIGS. 4 a, 4 b and 4 c)is glass that is visible light transmissive, it can be placed parallelto the micromirror array device (e.g. device 105 in FIGS. 4 a, 4 b and 4c) and the package substrate (e.g. package substrate 300).Alternatively, the cover substrate may be placed at an angle with themicromirror array device or the package substrate. Therefore, theinvention as described herein contemplates all such embodiments as maycome within the scope of the following claims and equivalents thereof.

1. A device package, comprising: a package substrate having firstsubstrate layer and second substrate layer; a cover; a glass fritproximate the cover and the second substrate layer; and a heaterlaminated between the first and second substrate layers proximate theglass frit, the heater operable to fuse the glass frit to the cover andsecond substrate layer.
 2. The package of claim 1, wherein the first andsecond substrate layers are ceramic materials.
 3. The package of claim1, further comprising: a microelectromechanical system device attachedto the package substrate.
 4. The package of claim 1, further comprising:an image detector or image sensor device attached to the packagesubstrate.
 5. The package of claim 1, further comprising: a CCD deviceattached to the package substrate.
 6. The package of claim 3, whereinthe microelectromechanical system device is a micromirror array devicehaving an array of deflectable reflective mirror plates.
 7. The packageof claim 6, wherein the mirror plates are enclosed within a spacebetween a device substrate that is transmissive to visible light and asemiconductor device substrate.
 8. The package of claim 7, wherein thesemiconductor device substrate comprises an array of electrodes fordeflecting the mirror plates.
 9. The package of claim 6, furthercomprising: a package cover substrate that is transmissive to visiblelight and is bonded to the package substrate such that the micromirrorarray device is enclosed within a space between the package cover andthe package substrate.
 10. The package of claim 1, wherein the packagecover substrate is hermetically bonded to the package substrate.
 11. Thepackage of claim 1, further comprising: a spatial light modulator deviceattached to the package substrate.